1. Field of the Invention
This invention generally relates to vehicle or robot locomotion, specifically to an improved and simplified system of using legs to propel a vehicle or robot.
2. Prior Art
Wheels, Legs, Obstacles, and Terrain
Human technology has had great success with vehicles on wheels. In practice wheeled vehicles need prepared roads because wheels do not perform well on terrain unless they are much larger than any irregularities of the terrain. For example, toy cars easily get stuck except on smooth, clean floors. Full-sized cars and trucks require a very expensive network of roads. Trains require smooth steel rails. Off-road vehicles typically have huge wheels to roll over irregularities, and still must proceed with careful attention to obstacles.
Tracked vehicles use continuous belts, usually of interlocking steel parts, rolling under wheels to improve the ability to roll over irregularities.
The Animal Kingdom makes use of legged locomotion in great variety, with many different numbers of legs, and different gaits. Legged locomotion can negotiate terrain with obstacles and irregularities almost as large as the length of the legs. Four legged animals in general and mountain goats in particular, easily negotiate large irregularities and step over obstacles.
Attempts have been made at mechanical walking, but there are few practical applications.
Complexity
In the prior art, technological attempts to mimic animal locomotion have been clumsy. Each leg on an animal typically has two or three joints (articulations) with one or two degrees of motion at each joint. Controlling these motions has proven difficult. Controlling them in such a way to overcome obstacles presents further difficulties. These issues are the subjects of the following U.S. patents.
U.S.Pat. No.InventorYearTitle6,481,513Buehler, et al.2002Single actuator per leg robotichexapod6,317,652Osada2001Legged mobile robot5,838,130Ozawa1998Locomotion control system of leggedmobile robot5,551,525Pack, et al.1996Climber robot5,351,626Yanagisawa1994Walking robot5,127,484Bares, et al.1992Orthogonal legged walking robotBalance vs. Complexity
Legged locomotion presents problems of balance, especially when the legs are few. With four, six, or more legs, balance is less of an issue because it is possible to have three feet on the ground at all times. However, controlling the many degrees of freedom becomes more of a problem.
Maintaining balance and negotiating terrain are the subjects of several patents.
These patents describe methods of balancing a bipedal robot.
6,959,776Furuta, et al.2005Bipedal humanoid5,459,659Takenaka1995Attitude stabilization control system fora legged mobile robot5,455,497Hirose, et al.1995Legged mobile robot and a system forcontrolling the same
The following patent describes a six-legged robot.
5,040,626Paynter1991Walking robots having double acting fluiddriven twistor pairs as combined joints andmotors and method of locomotionFlipping Upside Down
Practically all vehicles (legged and wheeled) and animals get into difficulty if they become flipped on their side or upside down. They have to work to right themselves in order to resume their locomotion. Vehicles typically must get help from an external source, such as a tow truck. This is usually a slow and clumsy operation.
Static Stability
To avoid flipping over, animals dynamically adjust the positions of their legs. Their sense of balance induces them to get a good footing. Wheeled vehicles typically do not employ this option.
Some wheeled vehicles employ a hybrid solution. Mobile cranes often have outrigger legs that they extend when stationary to improve stability.
High Speed Operation
Wheels perform well at high speeds.
Legs, however, typically have inertia that must be overcome to move them into place for the next step. This requires energy, introduces complexity, and causes wear on any articulations.
Absorbing Shocks and Steering
Practical wheeled vehicles need a compliant suspension to isolate them from the shocks and vibrations from any remaining irregularities in the road or surface, especially at high speeds. The suspension is often complex, expensive, and is a main determinant of vehicle performance. The need to steer the wheels adds another level of complexity to the suspension.
The Animal Kingdom has an advantage here because a leg by its nature incorporates its own suspension. The normal operation of the leg allows for movement that can absorb shocks.
In addition, animals typically can jump, by moving their legs with sufficient speed and energy. Similarly, steering is efficiently accomplished by control of the gait.
The following patent deals with absorbing shocks.
5,445,235Gomi, et al.1995Legged mobile robot equipped withimpact absorberMechanical Walking
Because of the difficulties mentioned above, mechanical walking is seen almost exclusively in experimental settings, and in toys, where the clumsiness and complexity are tolerable.
Tumbling Robots and Vehicles
Some robots or vehicles are built entirely inside a large wheel or sphere. The vehicle traverses ground by rolling or tumbling. Such a wheel is much larger than if the vehicle had 4 wheels, and is correspondingly good at overcoming obstacles and irregularities.
A conceptually simple way to make such a vehicle is to enclose an ordinary wheeled vehicle inside a large sphere or cylinder. It drives on its own smooth interior surface and carries that surface with it. The motion of the mass of the internal vehicle induces the sphere to roll.
Any spherical rolling vehicle suffers from very limited driving torque because there is no external body from which to drive (and brake) the sphere. Driving must be accomplished by internally moving the center of mass. The torque is limited to what can be achieved by moving a mass internally. This is especially a problem when braking suddenly. Locking the inside components of vehicle against the interior of the wheel will simply cause it to rotate with the wheel.
A tumbling vehicle presents problems for applications that require a stable platform. It would be a poor choice to carry human passengers. Instruments such as cameras, sensors, manipulator arms, and weapons often require a stable platform, and so are problematical for a tumbling vehicle.
The following patents describe tumbling vehicles.
6,786,495Browning2004Tumbling toy6,414,457Agrawal, et al.2002Autonomous rolling robot5,575,702Silvious1996Telescoping tumbling toy4,884,989Wong1989Toy for tumbling down verticalsurface